1. Field of the Invention
The present invention relates to a network accessing technique based on an ATM (Asynchronous Transfer Mode) technique and a DSL (Digital Subscriber Line) technique.
2. Description of the Related Art
With the rapid popularization of the Internet, the demand for quickly interconnecting end users and the Internet has been increasing.
FIG. 1 is a block diagram showing the configuration of a typical system for accessing the Internet.
An Internet backbone 2101 is directly connected with Web sites 2102, ftp sites 2103, enterprise LANs (Local Area Networks) 2104 with dedicated lines, and access points 2105 operated by Internet Service Providers (hereinafter referred to as ISPs).
Each general user (home user) or each user 2107 in a small enterprise makes a connection to a desired site via the Internet backbone 2101 by accessing an access point 2105 from a PC (Personal Computer) or a LAN via an access network 2106.
Since the Internet backbone 2101 and the access point 2105 are normally interconnected with a high-speed dedicated digital line, a fast access is ensured. In the meantime, the access network 2106 linking a user 2107 and an access point 2105 is typically a low-speed network such as a public telephone network, an ISDN (Integrated Services Digital Network), etc. in many cases, although a dedicated digital line network may be sometimes used.
However, it has become difficult for such a low-speed network to meet the rapidly increasing demand for the Internet in recent years. Especially, as a SOHO (Small Office/Home Office) becomes popular, the demand for quickly connecting a small-scale LAN to the Internet has been increasing.
Introduction of a new high-speed line infrastructure such as an optical fiber, etc. is a final solution in order to meet such demands. However, since this requires a lot of equipment investment, labor and time, it can hardly become a practical and short-term solution.
As a viable alternative, the DSL (Digital Subscriber Line) technique attracts public attention as a high-speed communications technique which uses telephone copper wire cables currently arranged in most homes and enterprises as they are and can coexist with communications using existing telephones.
The DSL technique is one type of modem technique. This technique includes methods such as an ADSL (Asymmetric DSL), an SDSL (Symmetric DSL), an HDSL (High bit rate DSL), a VDSL (Very high bit rate DSL), etc., which were developed for supporting various transmission rates, a symmetric/asymmetric communication, a modulation/demodulation method type, etc. These methods are generally referred to as an xDSL. The general term xe2x80x9cxDSLxe2x80x9d is hereinafter used in this specification.
With the xDSL technique, xDSL modems are arranged at both ends of an existing copper wire cable which links a subscriber home and an accommodation station of a common carrier. As a modulation/demodulation method in this case, any of three methods such as a 2B1Q (2 Binary 1 Quarternary), a CAP (Carrier-less Amplitude/Phase modulation), and a DMT (Discrete Multi-Tone) is adopted. With any of these modulation/demodulation methods, a high-speed communication of several-hundred to several-mega bits per second is made over a high-frequency band of approximately 30 KHz to 1 MHz.
As described above, the frequency bandwidth used in an xDSL communication differs from that of approximately 30 Hz to 4 KHz, which is used by a telephone speech signal. In such a case, a telephone speech signal and an xDSL signal can be multiplexed on one subscriber line by connecting circuits for different frequencies, which are referred to as splitters, to both of the xDLS modems within the subscriber home and within the common carrier. That is, in the subscriber home, the telephone and the xDSL modem are connected to the subscriber line via the splitter within the subscriber home. In the meantime, in the accommodation station, the existing telephone switch and the XDSL modem are connected to the subscriber line via a splitter within the accommodation station.
A collective modem which has a multiplexing capability and is referred to as a DSLAM (DSL Access Multiplexer) is mainly used as the xDSL modem within the accommodation station. With the DSLAM, xDSL signals from a plurality of xDSL lines are terminated by respective modem circuits, and the respectively terminated xDSL signals are multiplexed by a high-speed backbone interface. Use of such a DSLAM allows an xDSL line to be employed as a low-cost and high-speed access line leading to each type of backbone.
The above described backbone includes a dedicated line network, which is connected via a high-speed dedicated digital line interface and links headquarters and branch offices within an enterprise, the Internet connected via a LAN and a router, an ATM (Asynchronous Transfer Mode) network connected via an ATM interface such as a SONET interface, etc.
The technique for using the DSLAM as the front end of the ATM network among the above described techniques is expected to be a promising technique for implementing an ATM service on a global scale where common carriers tend to utilize a basic trunk line system in an ATM form. Furthermore, the ATM network is anticipated as a network for implementing the Internet backbone 2101 and the access network 2106, which are shown in FIG. 1. Considering this fact and the convenience where an existing copper wire cable can be used while maintaining a telephone service, it is significant that the xDSL line accommodated by the DSLAM is used as an access line to the ATM network or to the Internet.
In this case, an IP datagram transmitted, for example, from the PC or the LAN possessed by the user 2107 to the Web site 2102, is converted into an ATM cell and is further converted into an XDSL signal by the XDSL modem in the user 2107""s home.
The xDSL signal is transmitted to the copper wire cable which is the subscriber line via the splitter in the user 2107""s home, and reaches the accommodation station.
After the xDSL signal is split from a telephone speech signal by the splitter in the accommodation station, it is received by the DSLAM within the accommodation station.
The ATM cell received by the DSLAM is multiplexed with an ATM cell received from another subscriber line, and then transmitted to an ATM interface (such as a SONET interface) leading to the access network 2106 configured by the ATM network.
The ATM cell which has passed through the access network 2106 is received by an access server within the access point 2105. The access server extracts the IP datagram from the received ATM cell.
The extracted IP datagram is transferred to the Web site 2102 via the Internet backbone 2101.
To typically implement the connection to the Internet, the user 2107 first makes a point-to-point connection to the access server within the access point 2105 which is the entry to the Internet backbone 2101 by using a protocol referred to as a PPP (Point to Point Protocol). At this time, the user 2107 is assigned a global IP address which is determined according to a protocol referred to as an IP (Internet Protocol) and can be uniquely identified on the Internet, from a DHCP (Dynamic Host Configuration Protocol) server etc. belonging to an access server depending on need. Thereafter, the user 2107 stores the IP datagram including the IP address of an opposing server in a PPP packet by using a global IP address which is originally possessed by the user 2107 or is dynamically assigned, and exchanges the IP datagram with a server at a destination side.
In the meantime, for example, if two communicating devices make a communication in an ATM network, ATM addresses must be respectively assigned to both of the devices. At the same time, an ATM connection (VC: Virtual Connection/Channel) which can be uniquely identified within the ATM network must be established between the two devices.
Accordingly, with the technique for integrating the xDSL line, the ATM network, and the Internet, an ATM connection must be established based on the specification of ATM addresses between the xDSL modem within the user 2107 and the access server within the access point 2105 when a PPP session is started, as described above.
However, since the xDSL technique assumes that a high-speed communication is made at a low cost by directly linking an XDSL mode within a subscriber home and a DSLAM within an accommodation station, there is no concept of connecting/disconnecting an xDSL communication for each communication. Therefore, this technique does not work well with the control for establishing/releasing an ATM connection.
Accordingly, a dedicated line connection form where the access server within the access point 2105, the DSLAM within the accommodation station,. and the xDSL modem in the subscriber home are continuously connected with a PVC (Permanent Virtual Connection/Channel) was conventionally adopted in the network system where the xDSL line, the ATM network, and the Internet are integrated.
However, the same number of ATM connections as that of users 2107 are required in the above described conventional connection form, although general end users such as home users, etc. are not continuously connected to the Internet. Therefore, the connection resources (more specifically, the number of VPIs/VCIs or the bandwidth used by a switch) within the ATM network are fixedly and wastefully used, which leads to the inability of ATM networks being applied to a large number of subscribers.
An SVC (Switched Virtual Connection/Channel) which is a connection for each call may be applied to overcome this problem. However, because the connection form of the xDSL communication is assumed to be connectionless as described above, this communication does not work well with a connectionless SVC communication and an effective SVC controlling method does not currently exist.
The present invention was developed in the above described background, and aims at realizing a connection form where the connection resources within an ATM network can be efficiently used, when an xDSL line is connected to a particular destination such as an access server, etc. via a cell switching network such as an ATM network, etc.
One mode of the present invention assumes a method with which a subscriber side modem which performs modulation/demodulation with a digital subscriber line method accesses an access server connected to an ATM switch network by using ATM cells transferred with an asynchronous transfer mode method via an accommodation station side modem, which accommodates a digital subscriber line to which the subscriber side modem is connected.
The access server and the accommodation side modem are continuously connected by a permanent virtual connection.
Next, a virtual connection which is unused within the permanent virtual connection is managed in the access server and the accommodation station side modem.
The accommodation station side modem communicates with the access server based on a call originating request issued from the subscriber side modem, so that the unused virtual connection is allocated to the subscriber side modem.
According to the present invention, a PVC is established beforehand between an accommodation station side terminating device (modem) and an access server. The accommodation station side terminating device (modem) makes a communication with the access server based on the call originating request issued from the subscriber side terminating device (modem), so that an unused virtual connection is allocated to the subscriber side terminating device. As a result, the accommodation station side terminating device (modem) and the access server are continuously connected by the above described PVC, whereby the connection resources can be significantly reduced, a connection control can be dramatically simplified, and the response performance can be improved in comparison with the case where the accommodation station side terminating device and the access server are connected for each call.
Additionally, according to the present invention, the control for establishing/releasing a virtual connection within the PVC can be efficiently performed by using management and maintenance broadcast cells.
Furthermore, according to the present invention, the operation/non-operation of the accommodation station side modem can be controlled according to the operation/non-operation of the subscriber side modem, thereby preventing a waste of electric power when no communication is made.
Still further, according to the present invention, a line can be disconnected even if a link is disconnected without a proper process such as a process for powering down a modem or a PC.